JPH04331562A - Document copying machine - Google Patents

Abstract

PURPOSE: To accurately copy a document end by measuring a distance between an image of an original and a platen surface, obtaining a value indicating a focusing loss of image data from the platen surface based on the distance, and revising and correcting the image data based on the value. CONSTITUTION: In the case of the document copy mode, a height sensor 24 is operated to measure a distance ΔZ (distance between a platen surface 13 and pages of a book) of an object caused by the presence of a filing area 60 apart from an image of a book. In the correction of the image, a correction distance of an image segment in the scanning direction is expressed as Δx/cosθ, based on information from a height profile map, in which Δx is a projected distance of the image segment and θ is a local gradation. Thus, the image of a curved object, while being extended in the scanning direction, is projected on the flat platen surface. The correction such as above is attained by programming properly a processor to apply a correction factor to electric image data from a CCD 22.

Description

[Detailed description of the invention]

0001

FIELD OF THE INVENTION This invention relates to document copying machines, such as Xerox(R) copiers or printers, and more particularly to copying or scanning uneven originals such as bound books or three-dimensional objects. It concerns such a device with high performance for.

0002

2. Description of the Related Art Copying machines pose a problem when copying uneven originals, such as bound books, because it is difficult to copy information near the binding area of the book. It is. The difficulty in copying at the binding is that the portion of the book near the binding is raised above the image plane of the original, which is usually formed by a flat, transparent plate. The quality of the copy deteriorates with the distance of the original image from the image plane. The lack of sharpness and/or distortion in copies results from several factors: The factors are: 1) as the original is scanned in the central binding section, the projected image becomes increasingly out of focus; 2) the illumination of the spine becomes less than optimal; and 3) along the length of the scan. Compression of image data occurs along; 4
) As a result of the original image being placed at a certain angle to the image plane,
This causes deterioration in the clarity of image data; and so on.

Various approaches have been attempted to minimize or eliminate these factors. A common "force" approach is to force the book against the surface of the platen in order to minimize or prevent the binding portion from separating from the platen surface. but,
Page portions close to the binding portion remain at a shorter distance on the platen surface. As a result, the information contained in these portions is out of focus on the printed page. Furthermore, attempting to press the binding portion as close to the platen as possible may damage the binding portion of books, especially older books with fragile binding portions.

[0004] Another solution is to modify the platen so that the edges are sloping, so that the binding portion of the book is in the corner and the entire surface of the page being copied is in close contact with the platen surface. U.S. Patent No. 3,775,008
An example of this type of system is disclosed. These systems have several drawbacks. The range of magnification is limited because movement of the scanner at the edges of the beveled corners is restricted. Also, it is not possible to use a "split scan" system, which allows pages on both sides of the book to be placed on the platen and scanned without having to reposition the book.
Copying abilities are limited.

Yet another development is a system that employs a height sensor on the scanner to measure the height of the original image on the platen. Adjust the position of the visible image,
The height information is used to control the position of the scanning mirror to accommodate varying focus, control scanning speed, and control illumination. ``Document Copying Machine with High Book Copying Performance''(``DOKUMENT''), which was applied for on May 22, 1990
REPRODUCTION MACHIN WI
TH ENHANCED BOOK COPYI
U.S. patent application Ser. include. Although the above system overcomes many of the drawbacks mentioned above,
This requires precise mirror positioning and precise control of focusing lens and carriage speed. These elements add to the complexity of the device and increase its cost.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the photocopying of non-flat original images, such as books. Another object of the invention is to combine the convenience and functionality of split scan scanning with the accuracy of copying book edges.

It is another object of the present invention to provide a digital copying machine with minimal modifications to an otherwise standard digital copier.
The purpose is to achieve the above objectives.

[0008]

These and other objects are achieved by using a scanning system having a detector that detects the distance between an image plane and an image portion of the original remote from the image plane, and disadvantages are overcome. Image information obtained by an optical scanner is converted to electrical image data. Correction factors such as image position, image compression, image focus and image illumination are obtained from the data obtained from the height detection sensor, and these factors can be stored as an image map. The electrical image data is modified according to the correction element to correct or sharpen the electrical image data in portions of the original that are spaced apart from the image plane. Image height data can also be used to control scanning speed and illumination. The corrected and sharpened electrical image data is then sent to downstream imaging and printing equipment.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will now be described in detail with reference to the following figures, in which like reference numerals indicate like parts. Figure 1
shows a scanning system 10 operating in a conventional document scanning mode as well as a book copying mode. System 10 is positioned below a transparent image platen 12, which includes:
It is usually made of a hard, transparent material such as glass. Book 11 is shown mounted on top surface 13 of platen 12 . Top surface 13 forms the image surface of the original placed on platen 12 .

Scanning system 10 has a light source, such as a lamp 14 mounted inside a reflector 15. Radiant energy or light from lamp 14 is reflected upwardly through platen 12 and illuminates the original image placed on the platen. Scanning system 10 also includes a scanning mirror 16 positioned to receive visible light reflected from the original image. Lamp 14, reflector 15 and mirror 16 can be mounted in a common housing 17. Reflected optical image data received on scanning mirror 16 is directed through a suitable mirror assembly to optical imaging assembly 20, which is a simple, fixed focus optical imaging assembly 20. Model is preferred. Lens assembly 20 images the optical image information into a beam 19, which is directed to a suitable photosensor 22, which converts the optical image data of beam 19 into electrical image data. Ru. Although any known type of photosensor can be used, the preferred type is a charge coupled device (CCD).

[0011] Lamp 14, reflector 15, mirror 16, mirror assembly 18, lens assembly 20 and CCD 22 may be commonly mounted on a scanning carriage, indicated by dotted line C. Carriage C moves from left to right under the platen at a preset or controllable scanning speed. The scanning assembly performs a prescan movement to the left through the prescan zone, denoted PS, to provide acceleration (and vibration damping) prior to the start of the scan exposure cycle. The scanning start point is indicated by S0, and the scanning end point is indicated by S1.

Scanning assembly 10 also includes a height detector or sensor 24 that is located at the edge of an original document, such as a page of book 11, placed on surface 13 of platen 12. It is desirable to be positioned so as to scan along. In a preferred embodiment, detector 24 is, for example, an LE
A light emitting element such as D and a light receiving element such as a photodiode are built in. The LEDs produce a constant radiant output in an upward direction towards the platen 12 and the photodiode is positioned to receive the output of the LEDs reflected from the pages of the book 11. Such systems are used as autofocus sensors in cameras, but are also suitable for this application. Detector 24 is energized during the book copy mode to scan the book and generate a varying output signal, which may be affected by distance from the image plane of the book, such as the binding area 60. The resulting copy distance increase ΔZ (distance between the platen surface 13 and the book page) is shown. The output signal of detector 24 is used by computer 30 to generate image position, focus, image compression, and illumination correction signals, as described below. When set to book copy mode, height detector 2
4 is started and the deviation distance of the book page from the platen (Δ
Z) is measured. For the area where the book lies flat on the platen 12, the distance L is the distance from the scanning mirror to the surface 13 of the platen. For areas where the pages of the book are displaced from the platen surface 13, the distance L' is the sum of the distance L plus ΔZ at any particular location, for example as shown in FIG. Therefore, the detector 24
The output of indicates ΔZ at some given point. When the book's pages are flat on the platen, the distance ΔZ is zero and increases to a maximum value at the center of the book's binding area. Although detector 24 is shown as being in the same horizontal plane as scan mirror 16, it can also be vertically displaced by an appropriately offset distance used to obtain ΔZ.

In a typical operating cycle, scanner assembly 10 begins scanning from left to right at point S0. If desired, lamp 14 may be shock absorbing. As the scan progresses, the detector 24 continuously generates an output signal and sends it to the position signal generation circuit 26 (FIG. 2), in which the output signal is converted into a position signal proportional to the instantaneous value of L+ΔZ. converted. The output from position signal circuit 26 is sent to analog/digital converter 28. The digital signal is then provided to processor 32 of computer 30. The position signals are temporarily stored in memory unit 34 until scanning of both sides of the book is completed. Next, the point at which scanning ends (point S1
), a complete book height "profile" containing an approximation of the slope dz/dx is retrieved from memory 34 by processor 32 and required for image position, image focus, image compression, and image illumination. Information regarding the amount of correction is retrieved. Each of these corrections will be explained in more detail below.

The electrical image data signal from CCD 22 is converted by analog/digital converter 28;
A processor 32 of a computer 30 is provided. The correction factors described above, derived based on the signal from the height detector 24, are applied to the electrical image data by the processor 32, and the image data thus modified is transmitted to a downstream device such as an image controller or a printing press. Processing means are provided which use the modified electrical image data to create an output copy.

Image focus resulting from portions of the image remote from the image plane exceeding the depth of focus of the scanner's optical focusing mechanism is corrected by adding appropriate correction elements to the electrical image data. can do. One means of making this correction is to develop an empirical model of the depth of field characteristics of the particular imaging system being used. This property can be described as the pixel spread as a function of distance from the nominal image plane. The appropriate correction factors as a function of distance from the image plane can then be stored in memory 34 in the form of a look-up table. This appropriate element is then used in conjunction with the height information from the image profile to correct the faded image closer to its original sharpness. Mathematical techniques for correcting image degradation by altering electrical image data are already known and can also be implemented by programming processor 32 to make appropriate corrections. For such techniques, R
．． C. Gonzalez and P. Wintz
Co-author, Addison-Wesley Publi
Shining Co. Published by “Digital Image
Pocessing” 2nd edition.

Correction of image compression can be accomplished by modifying the electrical image data based on information from the height profile map. If the projection distance of an image segment in the scanning direction is Δχ and the local gradient is θ, then the correction distance of this segment is Δχ/cos θ
It is. The image is thereby extended in the scanning direction to project the entire curved object onto a flat image plane. Such corrections can be made by appropriately programming processor 32 to
This is achieved by adding a correction element to the electrical image data from CD 22.

By controlling the scanning speed of scanner assembly 10 as a function of the profile of the book, the angular It is also possible to control the compression of images resulting from the scanning of information from the spine 60 of a book placed with the book on. Referring to FIG. 2, processor 32 provides input to controller 36 using image profile information stored in memory 34. Referring to FIG. The control device 36 controls the scanning carriage drive device 4
This goal is achieved by controlling the speed of 0. In this case, the scanned portion of the image information in the portion of the image displaced from the image plane is slowed down by an amount proportional to the projected distance of that particular portion relative to its true distance. As a result, the image density is constant throughout the page, and the reason is that C
This is because the number of pixels per unit of true distance compiled by the CD 22 is constant. The calculation of the coefficient Δχ/cos θ is performed in processor 32 to derive control inputs to controller 36 to change the speed of carriage drive 40. Suitably programming the control inputs to controller 36 is within the skill of a designer of ordinary skill in the art, and detailed disclosure thereof is unnecessary.

Referring to FIG. 1 and considering the need for illumination correction, as the pages of the book are displaced from the platen surface 13, the illumination is effectively diminished (the output of the lamp 14 is no longer normally above the page). The reason for this is that the page moves away from the plane of optimal illumination. Therefore, in some systems, it may be necessary to ramp up and then ramp down the lamp power during a scan. Controlled by appropriate inputs from processor 32, controller 36 controls lamp power supply 42 to provide for or compensate for illumination fading.

Illumination correction can also be performed using a depth of focus model similar to the depth of focus model described in connection with imaging correction. In such a configuration, appropriate algorithms programmed into processor 32 may be used to restore gray pixels to white pixels as specified by the model. The extent to which gray is converted to white depends on the particular ΔZ distance at each scan position. Empirically deduced models can also be used. Such a model is stored in memory 34 in the form of a look-up table that provides a compensation factor that depends on the measured ΔZ. Other known mathematical techniques for correcting image degradation caused by illumination loss may also be implemented in processor 32.

Furthermore, compensation for slight deficiencies in illumination in region 60 can be achieved by combining two of the correction systems described above. For image information with some contrast, electrical image data enhancement by processor 32 can be used. In image areas where the image becomes darker, the illumination can be increased by increasing the power supply to the lamp 14. Based on the height data stored in memory 34, it is possible to switch from one correction system to another.

As previously noted, scanning mirror 16 is
in a fixed position, ideally around 45° to the scanning direction
Can be installed at an angle of Referring to FIG. 1, mirror 18
The principal ray (prin
ciple ray) is reflected by mirror assembly 18 through lens assembly 20 to CCD 22 . The image information received by the CCD in this manner accurately represents the original image data. However, if the chief ray reflects from a part of the original that is away from the image plane of the original, the optical path taken by the image ray changes by the value ΔZ, and the CCD
The light image 22 at 22 loses the focus set by the lens 20 provided the image is flat. However, the loss of optical focus can be compensated for by changing the electrical image information retrieved from the CCD 22. Moreover, the CCD provides a narrow optical window or "lens" that intersects the scanning direction. This element tends to provide properties similar to improving the depth of field of the optical system constituted by mirrors 16, 18 and lens 20. This is believed to enhance the focus of the system, at least in that part of the region 60 where the image is raised above the image plane. This latter effect will be explained with reference to FIG. 3, which shows pixels of image data S in a portion of the image that has emerged from the image plane 13. For each increment of scan ΔX, the edge of pixel S
They are located at different positions at distances ΔZ1 and ΔZ2 from 3. The average distance of the pixels from the image plane, ΔZ, is measured by the detector 24 and is used, as described above, to derive a value that provides an enhancement of the electrical image data. As mentioned above, the focus loss due to the change in optical path distance, which is represented by the difference between ΔZ1 and ΔZ2, is minimized by the system's unique solution caused by the use of CCD 22. In this way, the system compensates for image degradation resulting from the image being at an angular position relative to the image plane.

From the above description, it can be seen that the pre-scan mode provides maximum functionality. Microprocessor 30 is fully programmed to accept inputs for copy paper size, magnification, proofing, and simplex or duplex mode. All of these auxiliary inputs can be made following the pre-scan, but before the imaging scan begins. It is also possible at this time to input a suitable split scan algorithm that allows each page of the book to be copied onto a separate sheet of paper in single-sided or double-sided mode. In the split scan technique, height sensor 24 is used to measure area 60 of the dorsal portion. In the present invention, the microprocessor 3
Details of split-scan techniques that can be implemented by 0 are described in U.S. Pat. No. 4,659,207, the disclosure of which is incorporated herein by reference.

The main drawback of the pre-scan mode described above is the loss of processing time, ie the time required to perform the pre-scan. In other methods, detector 24 is scanned “on the f
In the disclosed system, this performance is improved because the processor 32 pulls out the correction elements almost instantaneously and the electrical The sensor portion of the detector 24 must be able to distinguish between the reflected light from the LED light source and the reflected light from the lamp 14 in this mode. , it is possible to use only the reflected lamp light and dispense with the need for a separate light source for real-time scanning mode.
4 needs to be located in the path of the reflected light from the lamp 14.

Although the invention finds greatest utility in the field of book copying, its principles apply to other types of copying, such as three-dimensional objects (of limited height and at each scanning position). (assuming a constant, i.e. dz/dx=0) and can also be applied to highly curved or folded documents.

[Brief explanation of drawings]

FIG. 1 is a schematic side view of a scanner showing scanning of a bound book.

FIG. 2 is a block diagram of a scanning and control system.

FIG. 3 is a diagram showing the imaging characteristics of the present system.

[Explanation of symbols]

10 Scanning system 11 Books 12 Image platen 14 Lamp 15 Reflector 16 Mirror 17 Common housing 20 Lens assembly 22 Photo sensor 24 Sensor

Claims (1)

[Claims] 1. A method for correcting a copy obtained from an image of a non-planar original having a portion in the image plane and a portion remote from the image plane; said method comprising: scanning said image of said original; generating electrical image data by imaging optical image data from said image onto a photosensitive element; an image of said original at a portion where said original image is away from said image plane; obtaining a value indicating the focus loss of the image data from a portion of the image away from the image plane based on the distance measured in the measuring step; and the step of correcting the electrical image data by changing the electrical image data according to the obtained value.